1. Field of the Invention
The present invention relates to a fuel cell having a matrix for holding an electrolyte and in particular to a layer-built structure and an installed structure of a fuel cell having a high capacity.
2. Description of the Prior Art
In a free-liquid surface type alkali fuel cell in which an alkaline aqueous solution is employed as an electrolyte, unit cells each of which comprises a chamber for containing an electrolyte and a pair of electrodes which sandwich the chamber therebetween are layered in the lateral direction so that the electrode surfaces are vertically arranged to thus form a fuel cell stack. On the other hand, a vertical layer-built fuel cell is the leading phosphoric acid type fuel cell in which phosphoric acid is employed as an electrolyte. The vertical layer-built fuel cell comprises unit cells, each of which comprises a matrix layer impregnated with phosphoric acid and a pair of electrodes, one of which is a hydrogen electrode, the other of which is an oxygen electrode and which sandwich the matrix layer therebetween and which are layered in the vertical direction so that the electrode surfaces are horizontally arranged to thus form a fuel cell stack. Presently, there has not been known any lateral layer-built phosphoric acid type fuel cell.
FIG. 8 is a perspective and partially cutaway view of a conventional fuel cell stack which is operated at normal pressure. In this fuel cell stack, unit cells 1, each of which comprises a pair of electrodes and a matrix holding phosphoric acid are sandwiched by the pair of electrodes. Grooved separators 2 are alternately arrayed to give a layered body 3. Both the upper and lower sides of the layered body 3 which is vertically layered are, respectively, sandwiched with a pair of collectors 5, insulating end plates 6 and fastening plates 7. A desired pressure is applied onto the surface of the layered body 3 by fastening studs 8 through the pair of fastening plates 7 to integrate the resulting assembly. A manifold for supplying and discharging a reaction gas is airtightly fitted to each of four side walls of the layered body 3. Grooves 4 are formed on either the upper or the lower surfaces of the separator 2 so as to be perpendicular to one another, one of which serves as a passage for a fuel gas and the other of which serves as a passage for an oxidizing agent. Thus, in the fuel cell of this type, a fuel gas and air as the oxidizing agent are supplied or discharged through an opening 9a for supplying and discharging the reaction gas formed on the manifold 9 at a pressure slightly higher than the atmospheric pressure, thereby producing electric power on the basis for an electrochemical reaction. In this respect, such phosphoric acid type fuel cell stacks have been developed which are capable of operating at normal pressure having an output power on the order to 50 kw, and generator plants are known which comprise four such fuel cell stacks connected in series or parallel at the electric circuit side and which have an output power on the order of 200 kw.
FIG. 9 is a perspective cross-sectional view of a conventional pressurized fuel cell. In this fuel cell, a fuel cell stack 10 contained in a pressure vessel 11 is fixed to and supported by a lower tank 12 having a shallow dish-like lower portion and upwardly covered with an upper hanging-bell type tank 13. After the lower tank and the upper tank are linked together through a flange, pressurized nitrogen gas is sealed in the pressure vessel 11, for instance, at a pressure on the order of about 4 atm and then the fuel cell is put into practical use. In addition to the fuel cell stack 10, there are connected, for instance, piping 15 for the air for reaction piping 16 for a fuel gas, and piping 17 for supplying cooling water to each corresponding cooling plate 14. The cooling plate 14 is inserted between two neighboring blocks, each comprising a plurality of unit cells and lead-out conductor 18 for outputting the generated electricity, which are all collected on the side of the lower tank 12 which supports the stack 10 and are externally taken out while airtightly passing through the lower tank 12. Moreover, the pressure of the reaction gases such as the fuel gas and the air for reaction is maintained at, for instance, about 4 atm so that it is in equilibrium with the pressure of the nitrogen gas. The output power of a single such pressure type fuel cell stack is known to be 260 kw and there have been known generator plants having an output power on the order of 1000 kw, which comprises four such stacks connected to one another in series or parallel through the external electric circuits. In addition, there are also known those obtained by horizontally arranging four vertical layer-built type fuel cell stacks in a pressure vessel in order to increase the output capacity.
The fuel cells per se which are stationary apparatuses do not cause vibrations at all, but they vibrate due to the influence of various external forces such as those encountered during transportation and earthquakes. On the other hand, the height of a fuel cell stack whose structural material mainly comprises a carbon material having an elastic coefficient on the order of not more than 1/10 times that of a steel plate which has a large capacity becomes almost 4 m. The resonant frequency of such a fuel cell stack is low and, there, if the stack vibrates, great bending strains, and stresses are generated. The vibration in turn leads to possible slippage of each unit cell and, in the worst case, breakage of the cell. Therefore, upon transportation of the vertically layered fuel cells, a large bending stress is applied to the layered body of unit cells, and this bending stress is liable to cause damages as the vehicles or ships move up and down if the fuel cells are transported while turning them sideways. On the other hand, if the fuel cells are transported in the standing state, the greater the height of the stacks, the greater the influence of the vibration of the stacks. On the other hand, with regard to the overland transportation, the height of loading is always limited to 3.4 m or less even when a trailer is provided which has a low deck body and, therefore, fuel cell stacks having a height on the order of up to 4 m cannot be transported by overland transportation.
On the other hand, as the development of the phosphoric acid type fuel cells proceeds, it has been desired to develop fuel cells having a greater capacity for use in generating electric power, but the overland transportation thereof is greatly restricted by the limitation on the height of loading. Therefore, the fuel cell stacks should be sub-divided into a large number of portions. This in turn leads to an increase in the production cost and in the space for installing the same. One means for solving this problem is to arrange four fuel cell stacks in a vertical cylindrical pressure vessel to thus give a module. In this way, only one pressure vessel is required and thus it is expected to make the production thereof more economical and to reduce the space for installing the stack. However, this approach cannot eliminate the limitations on the height thereof encountered during overland transportation, and thus the capacity thereof cannot be increased to a desired level.